1. The Field of the Invention
The present invention is related to compositions and methods for treatment of waste organic strippers which may also contain metals, such as copper. More particularly, the present invention is related to new compositions which are capable of removing waste organics and metals from stripper solutions in the form of easily processible precipitates.
2. Technical Background
The treatment of liquid and solid industrial and domestic waste has long presented numerous problems. With the development of more complex industries in densely populated areas, liquid waste has become an ever greater concern. In the past, liquid waste found its way freely into rivers, lakes, and other bodies of water. Treatment of such waste was minimal. Initially liquid waste did not present a significantly recognized problem, especially in areas such as lightly populated rural areas. As industry developed and became more complex, however, greater volumes of hazardous liquids required disposal. At the same time, awareness of the importance of scarce water and land resources increased as populations became more dense. For example, it was discovered that waste deposited years earlier was polluting ground water and causing numerous other problems.
In response to the health and environmental hazards produced by increases in potentially toxic waste, legislation was developed to govern the disposal of such waste. Various types of waste are regulated under federal and state environmental schemes, including disposal of waste water and disposal of both liquid and solid "toxic" or "hazardous" chemicals, as those terms are defined by statute and regulation.
As concern about disposal of liquid waste increased, technology began to address the problems involved. Various types of chemical and physical processes were developed to treat waste water. The most basic solution to liquid waste has been to simply allow suspended waste to settle out of the liquid. This is accomplished by placing the waste liquid in some type of settling pond and allowing the solids sufficient time to settle out. The clarified liquid is then separated from the solid layer.
In many contexts, it has been found desirable to accelerate the settling process. Thus, flocculating agents have been developed for addition to the polluted liquid. This "floc" combines with the suspended waste solids in a waste solution and accelerates the gravity settling of the solids. Common flocculating agents include alum (aluminum sulfate) and iron sulfate. These materials hydrolyze under weak acid to neutral conditions to form a sticky, gelatinous floc. This material accelerates the sedimentation of the solids suspended in the liquid.
More sophisticated treatments have also been developed for specific uses. Various chemical schemes and combinations of chemicals have been developed to suit particular needs. For example, polysilicic acid has been found to work as a flocculating agent in the presence of a water-soluble metal salt. It has also been discovered that certain combinations of magnesium and calcium ions aid in the treatment of degreasing and cleaning solutions. In one process, heavy metals are removed from industrial waste streams by use of ferric ions and an alkaline material at a basic pH. Other treatment methods employ magnetic processes to separate sludge materials. These and many other processes and materials have been used in attempts to treat various types of liquid wastes.
Unique problems are presented when it is necessary to treat waste liquids which include complex organic materials as well as heavy metals. One example is in the production of printed circuit boards where waste liquids are produced which include significant quantities of both organic materials and metals.
In typical processes, printed circuit boards are produced using a copper-clad substrate element of high dielectric strength which is coated with a photopolymer, called a "photoresist." The copper-clad substrate may begin the process of printed circuit board production by exposing the photoresist to electromagnetic radiation through a masking stencil. The radiation polymerizes the exposed areas, rendering those areas less soluble than the unexposed areas. The circuit board is then exposed to a developing agent. Upon contacting the developing agent, a reaction occurs with the non-exposed portions of the photopolymer, removing the photoresist from the copper surface. The exposed areas, conversely, are not removed from the surface. This produces a particular desired pattern.
In an alternative process, printed circuit boards may be made using a screening ink or liquid resist. In this process a photoreactive emulsion is screened onto the copper substrate to form an image of the desired pattern. The pattern is then screened onto the substrate by forming the image on a screen which forms as stencil. Ink is then applied to the stencil and a thin layer of the resist film is spread across the entire pattern. As a result, the image of the circuit pattern is transformed onto the copper coating on the substrate. The screen coating is cured and then etched. Following the etching steps, the ink is removed with an alkaline stripper solution.
It will be appreciated that liquid waste compositions remain following the production of printed circuit boards by either process. Both processes produce waste solutions which are complex and difficult to process. For example, the waste solution may include the organic stripper, the organic materials used in the process of preparing the printed circuit boards (such as inks, developing solution, and photoresists), as well as significant quantities of heavy metals originating from the board (principally copper and lead). The organic stripper is typically an organic solvent, such as butyl cellosolve (ethylene glycol monobutyl ether), together with various other optional components such as amines, surfactants, ketones, and the like. Thus, it will be appreciated that a very complex and potentially toxic waste is produced.
It has been found that it is not possible to treat this material with simple conventional treatment techniques. For example, processes such as ion exchange or continuous flow processes are not satisfactory. At the same time, governmental interest in regulation of disposal of this type of material is increasing. Thus, it is not generally possible to expose the material to conventional treatment techniques and then discharge the waste into municipal waster water systems or landfills. As is well appreciated, the production of waste that must be disposed of using particular regulated techniques greatly increases the cost of the process, resulting in higher prices for the product, and reduced profits for the manufacturer.
Agencies charged with environmental regulation have developed specific standards for disposal of solid and liquid wastes of this type. One common test is referred to as the Toxic Characteristic Leaching Procedure (TCLP). This test determines whether a waste solid is explosive, ignitable, corrosive, or if it is prone to leach harmful materials after disposal. Specifically, TCLP accesses the tendency of the waste material to leach over set time periods. If a material meets TCLP it is eligible for disposal in conventional landfills in that it is not likely to leach into ground or surface water. If a material fails to meet TCLP, it must be disposed of using expensive procedures required for toxic and hazardous materials.
In the present context, if the liquid waste is subjected to a flocculating agent, it would be very desirable for the resulting solid waste to avoid significant leaching once it is disposed of. This has been difficult to achieve with known techniques and materials. In addition, precipitates produced by known techniques are difficult to handle because of their physical and chemical characteristics. Such materials are typically sticky or gummy in consistency and, therefore, difficult to handle. These characteristics of the precipitates make them undesirable and increase the difficulty of disposal.
Similarly, there are also stringent standards for the disposal of liquid wastes. If the liquid waste contains significant toxic or hazardous materials, special processing is required. Such materials include specified organics and metals. The organics and metals contained within spent stripper solutions generally fall within the regulated classes. Conversely, if the liquid waste does not contain such materials, it can often be directly disposed of without processing, or by simply diluting the waste prior to disposal.
Thus, in the context of industrial processes in which complex liquid wastes are formed, it would be a significant advantage to render them disposable with conventional techniques. If it is necessary to resort to disposal methods specified for toxic and hazardous materials, the overall cost of the industrial process escalates significantly.
Accordingly, it would be a significant advancement in the art to provide methods and compositions for treating complex industrial wastes which contain both organic materials and heavy metals. More particularly, it would be a significant advancement in the art to provide such methods and compositions which rendered such wastes disposable by simple conventional techniques. It would be a further advancement in the art to provide methods and compositions which when added to such complex waste liquids would produce an easily handled solid material. It would be a related advancement in the art if the solid material was not prone to leaching once disposal occurred.
Such methods and compositions are disclosed and claimed herein.